The present invention relates to a discharge electrode for a laser device, and more particularly to the structure of the discharge electrode for the laser device.
A laser device which excites laser gases by electric discharge has been hitherto known and is shown, for example in U.S. Pat. No. 4,959,840. FIG. 12 is a sectional view of an excimer laser device 101 disclosed in the aforesaid Patent.
In FIG. 12, a pair of discharge electrodes 104 and 105 composed of an anode 104 and a cathode 105 are disposed facing each other with a predetermined space between them at predetermined positions inside a laser chamber 102 containing laser gases. In the excimer laser device 101, a high-voltage is applied to a space between the discharge electrodes 104 and 105 from a high-voltage power supply not illustrated to cause main discharge to occur, whereby the laser gases are excited to oscillate laser light.
A chamber opening 107 is disposed at the upper portion of the laser chamber 102, which is sealed up with insulating members 109 and 110 made of an insulating material such as a ceramic. A space between the laser chamber 102 and the insulating member 109 is sealed by an O-ring not illustrated. A cathode supporting member 108 made of a conductive material is attached to the insulating member 109 and the cathode 105 is fixed to the cathode supporting member 108.
A plurality of high-voltage feeder bolts 112 are screwed into the cathode supporting member 108, penetrating through base through-holes which are disposed in the insulating members 109 and 110 at predetermined intervals in a longitudinal direction. A high-voltage current for main discharge is supplied to the cathode 105 through these high-voltage feeder bolts 112.
FIG. 13 shows the bottom surface of the cathode supporting member 108. As shown in FIG. 13, cathode bolt holes 124, into which the high-voltage feeding bolts 112 are screwed, are disposed at predetermined intervals in the longitudinal direction in the cathode supporting member 108. At the bottom of the cathode 105, O-ring grooves 122 are disposed in such a manner to surround each of the cathode bolt holes 124. O-rings not illustrated are inserted inside the O-ring grooves 122 to seal the space between the cathode supporting member 108 and the insulating member 109.
However, the prior art disclosed in the aforesaid U.S. Pat. No. 4,959,840 has the following disadvantages.
Namely, in the prior art, as shown in FIG. 12 and FIG. 13, the O-ring groove 122 for scaling in the laser gases is provided to each of the high-voltage feeder bolt 112. Therefore, the interval between the high-voltage feeder bolts 112 is not allowed to be narrower than the outer periphery of the O-ring groove 122, and it is difficult to increase the number of the high-voltage feeder bolts 112.
Thereby, the high-voltage current flowing to each of the high-voltage feeder bolt 112 is increased and the discharge is easy to concentrate near the high-voltage feeder bolts 112 of the cathode 105 in main discharge. As a result, main discharge may be unstable and thus causing the disadvantage of variations occurring in the pulse energy of laser light for oscillating the pulse.
The present invention is made to eliminate the disadvantages in the aforesaid art, and its object is to provide a discharge electrode for a laser device which can cause stable main discharge to occur.
To attain the aforesaid object, the discharge electrode for the laser device according to the present invention has the structure including; a cathode base made of an insulating material for sealing up a chamber opening provided in a laser chamber for containing laser gases, a cathode attached to the cathode base with a bottom surface of the cathode in contact therewith, and a plurality of high-voltage feeder rods disposed in a longitudinal direction, penetrating through the cathode base from an outside of the laser chamber and supplying a high-voltage current to the cathode, and the structure in which an O-ring groove for sealing in the laser gases is formed on the bottom surface of the cathode to surround a plurality of holes for fixing the high-voltage feeder rods disposed on the bottom surface of the cathode.
According to the aforesaid structure, for a plurality of the high-voltage feeder bolts, one O-ring groove is used for sealing in the laser gases so that the intervals between the high-voltage feeder bolts are allowed to be narrower and the number of the high-voltage feeder bolts can be increased. Therefore, the high-voltage current flowing to each of the high-voltage feeder bolt is decreased and the high-voltage current is uniformly supplied to the cathode in the longitudinal direction. Thus, discharge concentrations are decreased and variations in pulse energy of laser light are decreased.
Moreover, the discharge electrode for the laser device may have the structure further including; a cathode bar in contact with the cathode on surfaces thereof, and the structure in which the high-voltage current is supplied to the cathode by means of the high-voltage feeder rod and the cathode bar.
According to the aforesaid structure, the high-voltage current is supplied to the cathode by contacting with surfaces thereof so that the high-voltage current is supplied more uniformly to the cathode in the longitudinal direction. As a result, the discharge concentrations are further decreased and the variations in the pulse energy of laser light are further decreased.